1. Field of the Invention
The present invention relates to an insert mounted on a cutting tool body and also relates to a cutting tool on which this insert is mounted.
2. Description of the Related Art
With a conventional cutting tool that uses an insert mounted on its tool body, a polygonal insert has been employed to make effective use of its corners so that as many positions in one insert as possible can be used. When an insert is mounted on a tool body, the insert is positioned so that it forms a positive axial rake angle, that is, a positive angle relative to the rotation axis of the tool body. Typically, when the axial rake angle becomes large, smooth cutting into a work piece can be realized at the time of cutting operations and the insert is able to execute cutting in more than one position, thereby enabling stable processing with little cutting vibrations. However, with the cutting tool on which the polygonal insert is mounted, it has been difficult to realize a large axial rake angle.
Examples of the polygonal insert are disclosed in, for example, Japanese Patent Laid-Open (Kokai) Publication No. HEI 7-246505, Japanese Patent Laid-Open (Kokai) Publication No. HEI 9-216113, and Japanese Patent (Kohyo) Publication No. HEI 11-513315.
An insert (throw-away insert) described in the Japanese Patent Laid-Open (Kokai) Publication No. HEI 7-246505 has a structure in which a minor cutting edge is provided at a position closer to one corner along an edge line between two corners, and a major cutting edge is provided that extends towards the other corner so that the major cutting edge forms an obtuse angle with the minor cutting edge. The major cutting edge slopes down from the other corner towards the minor cutting edge so as to make the distance to its seat face decrease gradually, and a minor cutting edge flank, which forms a positive relief angle, is provided on the side face extending from the minor cutting edge. Moreover, a first major cutting edge flank that extends from the major cutting edge is provided at the upper position of the side face extending from the major cutting edge, and this first major cutting edge flank is set to have a smaller relief angle than that of the minor cutting edge flank. Accordingly, it exerts no influence over the ability to cut at a right angle. Particularly, it is possible to improve the cutting blade strength of the major cutting edge portion and to extend the life of the insert chip.
An insert (throw-away insert) described in the Japanese Patent Laid-Open (Kokai) Publication No. HEI 9-216113 is structured in such a manner that: a relief angle of the insert in a substantially square shape is positive; as viewed from above, a cutting edge on its top face protrudes gradually from the corners on both ends towards the middle part; and, as viewed from the side of the throw-away insert, the cutting edge gradually slopes down towards the middle part from the corners on both ends. The same insert can be used even if the cutting tool is for left-handed use. Moreover, it is possible to finish off the cutting, even without any minor cutting edge, in such a manner that the bottom part of a work piece by making a right angle cut can form an approximate 90-degree angle with the side face of the work piece.
An insert described in the Japanese Patent (Kohyo) Publication No. HEI 11-513315 comprises a body part in a substantially rectangular column which has a top face, a bottom face, and at least two pairs of adjacent side faces. When viewed from above, a pair of corners along its diagonal line constitutes a cutting edge and the side faces extending respectively from the other pair of corners towards the corners constituting the cutting edges are receptacle surfaces to be received by a cutting tool.
Concerning the inserts described in the Japanese Patent Laid-Open (Kokai) Publication No. HEI 7-246505 and the Japanese Patent Laid-Open (Kokai) Publication No. HEI 9-216113, it is possible to set the axial rake angle to a larger value than the inclination angle of the major cutting edge. However, if the axial rake angle is set to this large value so as to realize smooth cutting into a work piece at the time of cutting operations, to allow sufficient improvement in cutting performance, and to realize sufficiently stable processing with almost no cutting vibrations, it becomes difficult to cause the envelope of the insert formed during the rotations of the cutting tool to constitute a cylindrical surface. Accordingly, it is still difficult to form a sufficiently large axial rake angle.
Concerning the insert described in the Japanese Patent (Kohyo) Publication No. HEI 11-513315, since, as viewed from above, a pair of corners along its diagonal line constitutes the cutting edges and the side faces extending respectively from the other pair of corners towards the corners constituting the cutting edges are the receptacle surfaces (referring to the fact that they are not cutting edges), the maximum cutting depth is shallow.